The present invention relates to the field of coaxial cable connectors for electronic imager assemblies, and more particularly to features for relieving strain on coaxial cables that connect an electronic imager assembly to a signal processor.
Coaxial cables have long been used to connect electrical devices to other electrical apparatus. A typical coaxial cable consists of an outer sheath enclosing a center conductor wire. The center conductor wire carries electrical signals, while the outer sheath provides electrical shielding. When such cables are used, it is well-known to provide some type of strain relief mechanism to alleviate stresses caused in the electrical connection between the coaxial cable wires and an interconnected electrical device. It is necessary that the strain relief provides adequate absorption of any pulling or twisting stresses placed on the coaxial cable wires in order to improve the reliability of the connection and prevent cable disconnection problems.
A particular field in which coaxial cables are used is that of medical or industrial imaging in which imaging devices such as endoscopes or borescopes utilize coaxial cables to connect different electrical devices with a miniature electronic imager and its associated circuitry.
For example, as shown in FIGS. 1, 2, and 12, a known video endoscopic apparatus 10, partially shown, typically employs a plurality of coaxial cables 12 to interconnect an electronic imager assembly 20 with a signal processor 13. The signal processor 13 receives the electrical signals produced by the electronic imager assembly 20 and processes the signals into a suitable video output signal. The signal processor 13 is connected to a video monitor 14, a video recorder 15, or other video peripheral device capable of handling the output video signal. The electronic imager assembly 20 shown in the FIGS. includes a miniature electronic imager 22, such as a CCD, having a transparent window 21 disposed over the image recording surface of the imager. A set of fine pitch imager leads 24 extend from between the miniature imager 22 and the window 21, extending to a pair of proximally located circuit boards 41, 42 each having a plurality of electronic components 35 disposed thereupon. A transmission cable 33 includes a plurality of coaxial cables 12 which are used to transmit power to the imager assembly 20 and to transmit an electrical signal, as conditioned by some of the components 35 on the circuit boards 41, 42 from the imager 22.
Referring more specifically to FIG. 12, the imager assembly 20 is mounted in the distal end of an insertion tube or section 17 relative to a lens system which may include one or more lens elements arranged to focus a target image upon the recording surface of the imager 22. A series of light emitting ends of a fiber bundle 16 are also disposed in proximity to the distal end of the insertion portion 17.
A problem is that though electronic imager assemblies have been streamlined and improved, particularly in terms of miniaturization and space savings, there has been relatively little development in providing strain relief for the coaxial cables used with such assemblies. For example, and still referring to FIGS. 1 and 2, one method of attaching the plurality of coaxial cables 12 to an electronic imager assembly 20 is provided by solder bonding the ends of each of the center conductor wires 19 of each of the coaxial cables 12 of the transmission cable 33 to traces 34 which are provided on facing surfaces of the pair of elongated circuit boards 41 and 42 which are held in spaced relation from one another. However, in this particular arrangement, the only strain relief is provided by the traces 34, which include only a relatively small surface area for contacting the center conductor wires 19 of the coaxial cables 12. However, as electronic imager assemblies continue to shrink in size to meet the target demand for such devices, such forms of strain relief mechanisms have proven inadequate for a variety of reasons.
The above known form of strain relief results in a very stiff distal end since the individual conductors of each coaxial cable 12 are forced apart by a block of resin material 45 and then soldered to the traces 34 in a manner that increases the length of the stiff portion of the assembly. The above solution increases the risk of breaking the connections between the coaxial cable and the assembly when the assembly is bent, twisted or pulled. It would be desirable to decrease the length of this stiff portion, and thereby provide improved flexibility.
Another problem with the above cable interconnection technique is that overall down sizing of endoscopes, borescopes, and other medical and non-medical video inspection instruments has caused the wires of the coaxial cables to become relatively thin and tiny, making these wires even more structurally weak. Utilizing an epoxy or resin to hold these wires is ineffective since their fragility tends to either break the wires completely, or cause them to pull out of the resin when twisted or pulled. Thus, it would also be very desirable to increase the strength of the connection between the wires and the assembly.
A further problem is that available space is limited, meaning conventional means of strain relief, such as clips or interconnect arrays, are highly impractical. Simply put, there is insufficient volume, particularly within an endoscope or borescope, to accommodate such designs. Moreover, there is a general need in the field to minimize the overall size of the insertion portion of these instruments so as to provide improved patient comfort and allow access to small spaces. Thus, it would also be desirable to decrease the volume of space occupied by the wire connector and the electronic imager assembly.
Still a further problem is that the structural components of electronic imager assemblies are also relatively thin and weak. This makes the entire assembly extremely difficult to handle, particularly during assembly of the insertion tube. Thus, there is a need to provide additional structural support to the components of the imager assembly. Moreover, during assembly, there is likelihood that the imager assembly may become misaligned at any time. Even slight misalignments of the imager may render the instrument unsuitable for use. Though applying an epoxy resin in the space between the two hybrid circuit boards prevents the circuit boards from moving apart or closer together, the imager itself is still prone to being misaligned. Thus, it would also be highly desirable to prevent misalignment of the imager itself.
Yet another problem is that the connectors, such as previously described in the above referred to ""313 patent, require many manufacturing steps to construct and consist of too many parts. For example, the connectors require hybrid boards that are bonded to a tapered block of resin encapsulating material.
In addition, once the endoscope is assembled, it is an extremely labor intensive, time consuming, and costly process to effect any repairs should they become necessary. As a result, a substantial need has arisen for a connector with an improved strain relief mechanism that is simple to construct and instal, and that will prevent coaxial cables from being detached or broken when placed under tension. Such a feature would vastly improve reliability and help ensure proper operation of the device.
It is therefore a primary object of the present invention to improve the state of the art of electronic imager assemblies.
It is still a further primary object of the present invention to improve the reliability of coaxial connection mechanisms for imaging instruments, such as endoscopes and borescopes.
It is yet another primary object of the subject invention to improve the integrity of the connection between coaxial cable wires and an electronic imager assembly.
According to a preferred aspect of the invention, a miniature wire connector is provided for relieving strain on coaxial cable wires electrically connected to circuit leads of an electronic imager assembly. The wire connector includes a substantially non-conductive body having a tapered construction. A plurality of grooves are formed on the body in which a layer of conductive plating is formed on at least a portion of each of the grooves. These grooves, formed in the outer surface of the non-conductive body, serve to retain at least a portion of the individual coaxial cable wires. The layer of conductive plating defines a conductive-portion, this plating layer being formed from a metallic or other electrically conductive material. Portions of the coaxial cable wires are placed within and connected to the grooves, with the center conductor wire of the cable being preferably soldered to the conductive-portion, and the conductive shield of the coaxial cable being preferably soldered to a different conductive-portion of the non-conductive body. The conductive shield may be a braided wire, serve wire, foil or plated conductive material.
The miniature wire connector may further include a recess formed in an upper or front surface of the body for fixedly retaining the electronic imager assembly. This recess includes at least one pair of substantially parallel attachment lugs used for bonding to the circuit leads of the electronic imager sensor assembly, and to fix that assembly in a stable position. The attachment lugs have at least one bonding surface for bonding to each of the hybrid circuit leads. The miniature wire connector may further include a cross-groove for providing an electrical connection to the outer sheath of the coaxial cable. The cross-groove is preferably filled with a conductive metal. The body of the wire connector may further include a fixturing hole therethrough for use during wire attachment.
The miniature wire connector is preferably used as part of a video inspection instrument, such as an endoscope or borescope. The video inspection instrument includes a tubular insertion portion capable of being positioned within a tortuous cavity, the instrument further having an optical system disposed within the insertion portion. The electronic imager assembly is disposed in relation to the optical system. According to the invention, the electronic imager assembly includes a miniature electronic imager having an image recording surface arranged to receive a focused optical signal from the optical system, a transparent window disposed over the image recording surface, and a plurality of fine pitch imager leads extending between the image recording surface and the transparent window. As noted above, the miniature wire connector is used to connect a transmission cable to the electronic imager assembly, the transmission cable including a plurality of coaxial cables. The video inspection instrument also may optionally include a plurality of electronic components for operating the miniature electronic imager, wherein at least a portion of the electronic components are substantially planarly disposed in relation to the optical system, thereby providing a compact assembly.
According to a second embodiment of the present invention, a miniature wire connector for connecting a transmission cable to an electronic imager assembly is provided.
The transmission cable is preferably the same design as that described above. In this embodiment, however, the miniature wire connector includes a substantially non-conducting center-conductor termination plate, retaining means defined in the center-conductor termination plate for retaining the electronic imager assembly on a first end surface thereof, and a plurality of grooves disposed along exterior surfaces of the center-conductor termination plate. Each of the grooves include an electrically conductive portion for retaining at least one center conductor wire of at least one individual coaxial cable, a shield termination plate, and a plurality of complementary grooves disposed along exterior surfaces of the shield termination plate for retaining a portion of a coaxial cable.
According to a third embodiment of the present invention, a miniature wire connector includes a substantially non-conducting supporting body. The wire connector, according to this embodiment, further includes retaining means defined in the supporting body for retaining an electronic imager assembly on a first end surface thereof, and a plurality of grooves disposed along exterior body surfaces for receiving at least one center conductor of at least one coaxial cable. According to this embodiment, each of the grooves has an electrically conductive portion for retaining at least a portion of at least one coaxial cable wire.
Another advantage of the present invention is that the layer of conductive plating in each groove of the described wire connector allows a large portion of the center conductor of the coaxial cable to be soldered to the conductive portion. Since more surface area of the center conductor is soldered to the groove, strain relief provided by the present connector is far superior to that of known connectors.
Yet another advantage of the present invention is that a more substantial length of the coaxial cable may be attached to the connector body.
Yet another advantage of the present invention is that the attachment lugs support and fixedly retain the sensor unit, the lugs also maintaining accurate alignment of the electronic imaging assembly.
Yet another advantage of the present invention is that the non-conductive body of the wire connector is formed using a minimum number of manufacturing and assembly steps.
Yet another advantage of the present invention is to allow for further imager assembly miniaturization.
Yet another advantage of the present invention is to allow the use of shielded and non-shielded wires.
These and other objects, features and advantages will be readily apparent from the following Detailed Description which should be read in conjunction with the accompanying drawings.